the circumstances and situations of the past to other people when they're asking about who you are.

当有人问起你的情况时，你可以用它向其他人描述过去的情况和经历。

I used to 课堂 - SpeakingMax英语口语达人

Or in situations where you have concern for your safety or for other's safety.

或者当你在为自己或他人的安危感到担忧时，都可以使用这个句型。

I'm worried 课堂 - SpeakingMax英语口语达人